Mechanical waves

The idea

Waves that require a material medium are mechanical waves, of two types: longitudinal, and transverse, in which particles vibrate perpendicular to the direction of propagation; sound is a mechanical wave.

Two ways to shake

A long row of particles carries a wave. In one case the particles shake along the row. In another they shake across the row.

A wave runs along the row from left to right. In which direction can the particles be shaken to pass it on?

• Along the row or across the row
• Just along the row
• Just across the row

Along or across

Choose a wave and press Play. Watch the red particle.

Needs a medium

Both waves need particles to pass the disturbance along. Waves that need a material medium are called mechanical waves. Sound is one of them.

Waves that require a material medium are mechanical waves. They are of two types: longitudinal waves and transverse waves, in which the particles vibrate perpendicular to the direction of propagation. Sound is a mechanical wave.

Notes

Mechanical waves need a material medium. They are longitudinal or transverse (particles vibrate perpendicular to propagation). Sound is a mechanical wave.

Check yourself

What is a mechanical wave?

In a transverse wave, how do the particles vibrate?

Mechanical waves are of two types. Which pair is correct?

Sound cannot propagate in a vacuum. Which fact explains this?

• A wave that can travel through a vacuum. Mechanical waves need a material medium. Without it they cannot propagate.
• A wave that requires a material medium for propagation — correct. Yes!
• A wave made by machines. A mechanical wave is defined by needing a material medium, not by how it is made.
• Parallel to the direction of propagation. Particles that vibrate parallel to the direction of propagation belong to a longitudinal wave.
• They do not vibrate. In both types of mechanical wave the particles vibrate. They differ in the direction of vibration.
• Perpendicular to the direction of propagation — correct. Yes!
• Longitudinal and transverse — correct. Yes!
• Compression and rarefaction. A compression and a rarefaction are regions in a sound wave. They are not types of wave.
• Source and medium. A source produces sound and a medium carries it. They are not types of wave.
• Sound is a transverse wave. Sound is a mechanical wave in which the particles vibrate parallel to the direction of propagation.
• Sound is a mechanical wave and needs a material medium — correct. Yes!
• A vacuum is too hot for sound. A vacuum is a space with no matter. Sound cannot travel there because it needs a material medium.